1. Field of the Invention
This invention relates to water disinfection, and, more particularly, to water disinfection using ultraviolet light.
2. Description of the Related Art
Water is an important resource that is used in many commercial purposes, such as agriculture and aquaculture, as well as for household use. Furthermore, clean water that is free from unhealthy chemicals and microorganisms is becoming a more precious resource as populations increase.
Water is often treated prior to it being used for commercial purposes or household use. Disinfection of the water to remove microorganisms is a common treatment. The use of ultraviolet (xe2x80x9cUVxe2x80x9d) light as a disinfecting agent is not a new idea. Downs and Blunt discovered that sunlight destroyed some bacteria in 1878. Since their discovery, scientists have performed experiments to determine the conditions when UV radiation can be used as a disinfecting agent, and have determined the doses required to kill many microorganisms. Disinfection is generally accomplished using heat, chemicals, or UV light. UV light is particularly desirable since it leaves no toxic residue in the water.
The prior art has many applications of treating water with UV light to kill microorganisms. These applications involve flowing water going past a UV light source. In some applications, water flows past a bank of light sources. This application is problematic as the light sources may be extremely heavy, making them difficult to replace. In another application, a UV light source is suspending axially in a pipe and water flows past it. The maintenance of this type of light source may also be difficult. Some problems are common to both applications. The light sources become fouled with use from being in continual contact with the water flow, thereby reducing the efficiency of the light sources. Further, the UV light is often not efficiently absorbed by the water. Instead, the UV light is absorbed by the walls of the vessels in which the UV lights are disposed Therefore, a water disinfection system using UV light that does not incur fouling of the light source and has efficient absorption of the UV light by water is needed. It is further needed a system that permits quick and simple maintenance of the UV light source.
In an aspect of the invention, a water disinfection system comprises a vertical water column directing channel and an ultraviolet light beam generator system. The vertical water column directing channel has an open top end and a channel interior space extending from the open top end. The ultraviolet light beam generator system has an ultraviolet light beam exit. The ultraviolet light beam generator system is arranged such that an ultraviolet light beam generated therein exits through the ultraviolet light beam exit, passes through the channel top open end, and enters the channel interior space.
In a further aspect of the invention, the channel open top end comprises a top end interior cross-section. Additionally, the ultraviolet light beam produced by the ultraviolet light beam generator system has a light beam cross section that is the substantially the same as the top end interior cross-section or eclipses the top end interior cross-section.
In a further aspect of the invention, the ultraviolet light beam produced by the ultraviolet light beam generator system comprises ultraviolet light in a spectral band of approximately 242 nm to 270 nm.
In a further aspect of the invention, the vertical water column directing channel comprises a riser having a length from the open top end to a bottom end and a substantially constant interior cross-section through the riser length. The top end interior cross-section is generally equal to the riser interior cross-section. In a still further aspect of the invention, the riser is generally cylindrical in shape.
In a further aspect of the invention, a water column turbulating feature located at the channel top open end. In a still further aspect of the invention, the water column turbulating feature is one or more notches in the vertical water column directing channel at the open top end.
In a further aspect of the invention, the vertical water column directing channel comprises an untreated water entrance into the channel""s interior space. The channel""s interior space also comprises a channel interior space portion being defined by the top open end and the untreated water entrance. The channel interior space portion has a continuous volume therein with a constant latitudinal cross-section and an axial length extending from the open top end and through the channel interior space portion. Further, the ultraviolet light beam generator system is arranged such that the ultraviolet light beam is directed through the open top end along the channel interior space portion continuous volume.
In a still further aspect of the invention, the ultraviolet light beam has a water absorption distance that is less than the continuous volume axial length. As a result, the ultraviolet light beam is substantially absorbed by water flowing through the vertical water column directing channel and not by the vertical water column directing channel.
In a further embodiment of the invention, the ultraviolet light beam generator system comprises a lamp and a reflector. The lamp produces dispersed light to be used to form the ultraviolet light beam. The reflector may be parabolic or elliptical and positioned to direct the dispersed light from the lamp. In a still further aspect of the invention, the lamp is a medium pressure mercury arc lamp. In an aspect of the invention, the ultraviolet light beam generator system comprises a fiber optic system.
In a further aspect of the invention, there may be a plurality of vertical water column directing channels. The ultraviolet light beam generator system comprises a plurality of ultraviolet light beam exits. The ultraviolet light beam generator system is arranged such that ultraviolet light beams generated therein exit through the ultraviolet light beam exits, pass through the channels top open ends and enter the channels interior spaces. A lamp in ultraviolet light beam generator system may generate the ultraviolet light beams for more than one exit and/or riser.
In a further aspect of the invention, an uninterrupted air space is disposed between the channel open top end and the ultraviolet light beam exit of the ultraviolet light beam generator system. In this case, the water has limited, if substantially non-existent, opportunities to contact the surface of the exit and start fouling it.
In an aspect of the invention, a process of disinfecting water comprises the steps of forming a vertically oriented column of flowing water to be disinfected and directing an ultraviolet beam into the column. The flowing water moves from a bottom of the column to a top of the column, at which point the flowing water flows in a general radial direction away from the column top. The ultraviolet light beam is directed through an uninterrupted air space, the flowing water column top and into the column of water. The ultraviolet light beam disinfects the flowing water prior to the flowing water flowing away from the flowing water column top
In a further aspect of the invention, the column of flowing water is formed by directing the flowing water through a vertically oriented channel. In a still further aspect of the invention, the vertically oriented channel is a cylindrical riser.
In a further embodiment of the invention, the light beam is collimated and has a latitudinal cross-section generally the same as, or bigger than, a latitudinal cross-section of the flowing water column top. Further, the collimated ultraviolet light beam is aligned with the column of flowing water such that the collimated ultraviolet light beam is generally coincident with the column of flowing water after the collimated ultraviolet light beam passes through the flowing water column top.
In a further aspect of the invention, the light beam. is substantially absorbed by the column of flowing water.
In a further aspect of the invention, a volumetric flow rate of the column of flowing water and an intensity of the ultraviolet light beam is chosen to achieve a predetermined microorganism survival rate. In a still further aspect of the invention, the using a microorganism survival equation, the microorganism survival equation is:
N1/N0=exe2x88x92k(It)
where
N1=Final number of living organisms
N0=Initial number of living organisms
xe2x88x92k=rate constant
I=Intensity of the ultraviolet light beam (mW/cm2)
t=time required to achieve the desired kill percentage
and the volumetric flow rate of the column of flowing water is a light absorbance volume divided by t, wherein the light absorbance volume is a volume of the column of flowing water in which substantially all of the ultraviolet light beam is absorbed.